if not modules then modules = { } end modules ['math-vfu'] = {
    version   = 1.001,
    comment   = "companion to math-ini.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

-- somehow an italic gets passed for 'next'

-- All these math vectors .. thanks to Aditya and Mojca they become better and
-- better. If you have problems with math fonts or miss characters report it to the
-- ConTeXt mailing list. Also thanks to Boguslaw for finding a couple of errors.

-- Although this mechanism was a candidate for obsolence, the fact that Iwona and
-- Antykwa are nice fonts (especially for display) I decided to keep it around but
-- in a bit upgraded way. It is also a test for virtual tfm/pfb fonts that we keep
-- around but hardly gets tested. However, much is still pretty old code, dating
-- from when we emulated \UNICODE\ math and \OPENTYPE\ math fonts using traditional
-- fonts.

-- Musical timestamp: Januari 2023 Riverside ID.Entity release date, after all we
-- only use the following code for ther Polish Iwona, Kurier and Antykwa fonts.

local type, next, tonumber = type, next, tonumber
local max = math.max
local fastcopy, sortedhash = table.copy, table.sortedhash

local fonts, mathematics = fonts, mathematics

local trace_virtual = false  trackers.register("math.virtual", function(v) trace_virtual = v end)
local trace_timings = false  trackers.register("math.timings", function(v) trace_timings = v end)

local add_optional  = false  directives.register("math.virtual.optional",function(v) add_optional = v end)

local report_virtual    = logs.reporter("fonts","virtual math")

local allocate          = utilities.storage.allocate
local setmetatableindex = table.setmetatableindex
local formatters        = string.formatters

local chardata          = characters.data

local mathencodings     = allocate()
fonts.encodings.math    = mathencodings -- better is then: fonts.encodings.vectors
local vfmath            = allocate()
fonts.handlers.vf.math  = vfmath

local helpers           = fonts.helpers

local addprivate        = helpers.addprivate
local hasprivate        = helpers.hasprivate
local vfcommands        = helpers.commands

local rightcommand      = vfcommands.right
local leftcommand       = vfcommands.left
local downcommand       = vfcommands.down
local upcommand         = vfcommands.up
local push              = vfcommands.push
local pop               = vfcommands.pop
local slotcommand       = vfcommands.slot
local staycommand       = vfcommands.stay

local nps = fonts.helpers.newprivateslot
local ps  = fonts.helpers.privateslot

nps("rule middle piece")
nps("rule right piece")
nps("rule left piece")
nps("double rule middle piece")
nps("double rule right piece")
nps("double rule left piece")
nps("arrow left piece")
nps("arrow right piece")
nps("double arrow left piece")
nps("double arrow right piece")

nps("flat rule left piece")
nps("flat rule middle piece")
nps("flat rule right piece")

nps("flat double rule left piece")
nps("flat double rule middle piece")
nps("flat double rule right piece")

nps("minus rule left piece")
nps("minus rule middle piece")
nps("minus rule right piece")

do

    -- this overlaps with math-act

    local function horibar(main,unicode,rule,left,right,normal,force,m,l,r)
        local characters = main.characters
        local data       = characters[unicode]
        if force or not data then
            local height = main.mathparameters.defaultrulethickness or 4*65536/10
            local f_rule = rule and formatters["M-HORIBAR-M-%H"](rule)
            local p_rule = rule and hasprivate(main,f_rule)
            local ndata  = normal and characters[normal]
            if rule and left and right and normal then
                local ldata  = characters[l or left]
                local mdata  = characters[m or rule]
                local rdata  = characters[r or right]
                local lwidth = ldata.width or 0
                local mwidth = mdata.width or 0
                local rwidth = rdata.width or 0
                local nwidth = ndata.width or 0
                local down   = (mdata.height / 2) - height
if unicode == normal then
    height = ndata.height
    down   = 0
end                --
                local f_left  = left  and formatters["M-HORIBAR-L-%H"](left)
                local f_right = right and formatters["M-HORIBAR-R-%H"](right)
                local p_left  = left  and hasprivate(main,f_left)
                local p_right = right and hasprivate(main,f_right)
                --
                if not characters[p_rule] then
                    p_rule = addprivate(main,f_rule,{
                        height   = height,
                        width    = .95*mwidth,
-- keepvirtual      = true,
                        commands = {
                            push,
                            leftcommand[.025*mwidth],
                            downcommand[down],
                            slotcommand[0][m or rule],
                            pop,
                        },
                    })
                end
                if not characters[p_left] then
                    p_left = addprivate(main,f_left,{
                        height   = height,
                        width    = .95*lwidth,
-- keepvirtual      = true,
                        commands = {
                            push,
                            leftcommand[.025*lwidth],
                            downcommand[down],
                            slotcommand[0][l or left],
                            pop,
                        },
                    })
                end
                if not characters[p_right] then
                    p_right = addprivate(main,f_right,{
                        height   = height,
                        width    = .95*rwidth,
-- keepvirtual      = true,
                        commands = {
                            push,
                            leftcommand[.025*rwidth],
                            downcommand[down],
                            slotcommand[0][r or right],
                            pop,
                        },
                    })
                end
if unicode ~= normal then
                data = {
                    unicode  = unicode,
                    height   = height,
                    width    = nwidth,
                    commands = {
                        downcommand[down],
                        slotcommand[0][normal]
                    },
                }
                characters[unicode] = data
end
                data.parts = {
                    { glyph = p_left, ["end"] = 0.4*lwidth },
                    { glyph = p_rule, extender = 1, ["start"] = mwidth, ["end"] = mwidth },
                    { glyph = p_right, ["start"] = 0.6*rwidth },
                }
            else
                local width = main.parameters.quad/2 or 4*65536 -- 3
                if not characters[p_rule] then
                    if unicode == normal then
                        p_rule = addprivate(main,f_rule,{
                            height   = ndata.height,
                            width    = width,
                            commands = {
                                push,
                                upcommand[(ndata.height - height)/2],
                                { "rule", height, width },
                                pop
                            },
                        })
                    else
                        p_rule = addprivate(main,f_rule,{
                            height   = height,
                            width    = width,
                            commands = {
                                push,
                                { "rule", height, width },
                                pop
                            },
                        })
                    end
                end
if unicode ~= normal then
                data = {
                    unicode  = unicode,
                    height   = height,
                    width    = width,
                    commands = {
                        slotcommand[0][p_rule]
                    }
                }
                characters[unicode] = data
end
                data.parts = {
                    { glyph = p_rule, ["start"] = width/2, ["end"] = width/2 },
                    { glyph = p_rule, extender = 1, ["start"] = width/2, ["end"] = width/2 },
                }
            end
            data.keepvirtual = true -- i need to figure this out
            data.partsorientation = "horizontal"
        end
    end

    -- local rootbarmiddle -- false = addprivate(main,formatters["M-R-%H"](next))
    -- local rootbarright  -- false = addprivate(main,formatters["M-R-%H"](next))

    local function rootbar(main,unicode,rule,right,normal)
        local characters = main.characters
        if not characters[unicode] then
            local height = main.mathparameters.defaultrulethickness or 4*65536/10
            if rule and right and normal then
                local mdata  = characters[rule]
                local rdata  = characters[right]
                local ndata  = characters[normal]
                local mwidth = mdata.width or 0
                local rwidth = rdata.width or 0
                local nwidth = ndata.width or 0
                local down   = (mdata.height / 2) - height
                --
                local f_rule  = rule  and formatters["M-ROOTBAR-M-%H"](rule)
                local f_right = right and formatters["M-ROOTBAR-R-%H"](right)
                local p_rule  = rule  and hasprivate(main,f_rule)
                local p_right = right and hasprivate(main,f_right)
                --
                if not p_rule then
                    p_rule = addprivate(main,f_rule,{
                        height   = height,
                        width    = .95*mwidth,
                        commands = {
                            push,
                            leftcommand[.05*mwidth],
                            downcommand[down],
                            slotcommand[0][rule],
                            pop,
                        },
                    })
                end
                if right and not p_right then
                    p_right = addprivate(main,p_right,{
                        height   = height,
                        width    = .95*rwidth,
                        commands = {
                            push,
                            leftcommand[.05*rwidth],
                            downcommand[down],
                            slotcommand[0][right],
                            pop,
                        },
                    })
                end
                characters[unicode] = {
                    keepvirtual      = true,
                    partsorientation = "horizontal",
                    height           = height,
                    width            = rwidth,
                    commands         = {
                        slotcommand[0][p_right],
                    },
                    parts            = {
                        { glyph = p_rule, extender = 1, ["start"] = mwidth, ["end"] = 0.9*mwidth },
                        { glyph = p_right, ["start"] = 0.6*rwidth },
                    }
                }
            end
        end
    end

    local function parent(main,unicode,first,rule,last,where)
        local characters = main.characters
        local chardata   = characters[unicode]
        if characters[unicode] then
            local template = characters[first]
            if template then
                local crule   = characters[rule]
                local xheight = main.mathparameters.xheight
                local rheight = 0
                local rdepth  = 0
--                 if crule then
--                     rheight = crule.height
--                     rdepth  = crule.depth
--                 else
                    local width   = template.width / 4
                    local height  = template.height
                    local depth   = template.depth
                    rheight = where == "top" and   height or 3*height
                    rdepth  = where == "top" and 2*height or 0
                    characters[rule] = {
                        height   = rheight,
                        depth    = rdepth,
                        width    = width,
                        commands = { push, { "rule", height, width }, pop },
                    }
--                 end
                characters[first].depth = rdepth
                characters[last] .depth = rdepth
                if where == "top" then
                    while true do
                        chardata.height  = chardata.height - xheight
                        chardata.depth   = 0
                        chardata.yoffset = -xheight
                        local next = chardata.next
                        if next then
                            unicode  = next
                            chardata = characters[unicode]
                        else
                            break
                        end
                    end
                else
                    while true do
                        chardata.height  = 0
                        local next = chardata.next
                        if next then
                            unicode  = next
                            chardata = characters[unicode]
                        else
                            break
                        end
                    end
                end
                chardata.keepvirtual      = true
                chardata.partsorientation = "horizontal"
                chardata.parts            = {
                    { glyph = first },
                    { glyph = rule, extender = 1, start = width/2, ["end"] = width/2 },
                    { glyph = last  },
                }
            end
        end
    end

    local function brace(main,unicode,first,rule,left,right,rule,last,where)
        local characters = main.characters
        local chardata   = characters[unicode]
        if chardata then
            local template = characters[first]
            if template then
                local xheight = main.mathparameters.xheight
                local width   = template.width / 4
                local height  = template.height
                local depth   = template.depth
                local rheight = 3*height
                local rdepth  = 2*height
                characters[rule] = {
                    height   = rheight,
                    depth    = rdepth,
                    width    = width,
                    commands = { push, { "rule", height, width }, pop },
                }
                -- don't change snippets, they serve dual purposes
                if where == "top" then
                    while true do
                        chardata.height  = chardata.height - xheight
                        chardata.depth   = 0
                        chardata.yoffset = -xheight
                        local next = chardata.next
                        if next then
                            unicode  = next
                            chardata = characters[unicode]
                        else
                            break
                        end
                    end
                else
                    while true do
                        chardata.height = 0
                        local next = chardata.next
                        if next then
                            unicode  = next
                            chardata = characters[unicode]
                        else
                            break
                        end
                    end
                end
                chardata.keepvirtual = true
                chardata.partsorientation = "horizontal"
                chardata.parts            = {
                    { glyph = first },
                    { glyph = rule, extender = 1, start = width/2, ["end"] = width/2 },
                    { glyph = left  },
                    { glyph = right },
                    { glyph = rule, extender = 1, start = width/2, ["end"] = width/2 },
                    { glyph = last  },
                }
            end
        end
    end

    local function dots(main,unicode)
        local characters = main.characters
        local c = characters[0x002E]
        if c then
            local w         = c.width
            local h         = c.height
            local d         = c.depth
            local size      = main.parameters.size
            local mu        = size/18
            local right3mu  = rightcommand[3*mu]
            local right1mu  = rightcommand[1*mu]
            local up1size   = upcommand[.1*size]
            local up4size   = upcommand[.4*size]
            local up7size   = upcommand[.7*size]
            local right2muw = rightcommand[2*mu + w]
            local slot      = slotcommand[0][0x002E]
            if unicode == 0x22EF then
                local c = characters[0x022C5]
                if c then
                    local width  = c.width
                    local height = c.height
                    local depth  = c.depth
                    local slot   = slotcommand[0][0x022C5]
                 -- local stay   = staycommand[0x022C5]
                 -- local right3mu  = rightcommand[width+3*mu]
                    characters[unicode] = {
                        width    = 3*width + 2*3*mu,
                        height   = height,
                        depth    = depth,
                        commands = {
                            slot, right3mu, slot, right3mu, slot,
                         -- push, slot, right3mu, slot, right3mu, slot, pop,
                         -- stay, right3mu, stay, right3mu, stay,
                        }
                    }
                end
            elseif unicode == 0x22EE then
                characters[unicode] = {
                    width    = w,
                    height   = h+0.8*size,
                    depth    = 0,
                    commands = {
                     -- push, push, slot, pop, up4size, push, slot, pop, up4size, slot, pop,
                        push, slot, pop, up4size, push, slot, pop, up4size, slot,
                    }
                }
            elseif unicode == 0x22F1 then
                characters[unicode] = {
                    width    = 3*w + 6*size/18,
                    height   = h+0.7*size,
                    depth    = 0,
                    commands = {
                     -- push,
                        right1mu,
                        push, up7size, slot, pop,
                        right2muw,
                        push, up4size, slot, pop,
                        right2muw,
                        push, up1size, slot, pop,
                        right1mu,
                     -- pop
                    }
                }
            elseif unicode == 0x22F0 then
                characters[unicode] = {
                    width    = 3*w + 6*size/18,
                    height   = h+0.7*size,
                    depth    = 0,
                    commands = {
                     -- push,
                        right1mu,
                        push, up1size, slot, pop,
                        right2muw,
                        push, up4size, slot, pop,
                        right2muw,
                        push, up7size, slot, pop,
                        right1mu,
                     -- pop
                    }
                }
            else
                characters[unicode] = {
                    width    = 3*w + 2*3*mu,
                    height   = h,
                    depth    = d,
                    commands = {
                     -- push, slot, right3mu, slot, right3mu, slot, pop,
                        slot, right3mu, slot, right3mu, slot,
                    }
                }
            end
        end
    end

    local function jointwo(main,unicode,u1,d12,u2)
        local characters = main.characters
        local c1 = characters[u1]
        local c2 = characters[u2]
        if c1 and c2 then
            local w1 = c1.width
            local w2 = c2.width
            local width
            if d12 == false then
                d12   = 0
                width = w2
            elseif d12 < 0 then
                d12   = d12 * w2
                width = w2
            else
                d12   = d12 * main.parameters.size/18 -- mu
                width = w1 + w2 - d12
            end
            characters[unicode] = {
                unicode  = unicode,
                width    = width,
                height   = max(c1.height or 0, c2.height or 0),
                depth    = max(c1.depth  or 0, c2.depth  or 0),
keepvirtual = true,
                commands = {
                 -- { "inspect" },
                 -- { "trace" },
                    slotcommand[0][u1],
                 -- { "trace" },
                    d12 ~= 0 and leftcommand[d12] or false,
                    slotcommand[0][u2],
                 -- { "trace" },
                },
            }
        end
    end

    local function overlaytwo(main,unicode,u1,factor,u2) -- not ...
        local characters = main.characters
        local c1 = characters[u1]
        local c2 = characters[u2]
        if c1 and c2 then
            local width = c2.width
            characters[unicode] = {
                width    = width,
                height   = max(c1.height or 0, c2.height or 0),
                depth    = max(c1.depth  or 0, c2.depth  or 0),
                commands = {
                    push,
                    slotcommand[0][u2], -- =
                    pop,
                    factor ~= 0 and rightcommand[factor*width] or false,
                    slotcommand[0][u1], -- /
                },
            }
        end
    end

    local function jointhree(main,unicode,u1,d12,u2,d23,u3)
        local characters = main.characters
        local c1 = characters[u1]
        local c2 = characters[u2]
        local c3 = characters[u3]
        if c1 and c2 and c3 then
            local w1 = c1.width
            local w2 = c2.width
            local w3 = c3.width
            local ds = main.parameters.size/18
            d12 = d12 * ds
            d23 = d23 * ds
            characters[unicode] = {
                unicode  = unicode,
                width    = w1 + w2 + w3 - d12 - d23,
                height   = max(c1.height or 0, c2.height or 0, c3.height or 0),
                depth    = max(c1.depth  or 0, c2.depth  or 0, c3.depth  or 0),
                commands = {
                 -- push,
                    slotcommand[0][u1],
                 -- pop,
                    d12 ~= 0 and leftcommand[d12] or false,
                 -- push,
                    slotcommand[0][u2],
                 -- pop,
                    d23 ~= 0 and leftcommand[d23] or false,
                 -- push,
                    slotcommand[0][u3],
                 -- pop,
                }
            }
        end
    end

    local function stack(main,unicode,u1,d12,u2)
        local characters = main.characters
        local c1 = characters[u1]
        if not c1 then
            return
        end
        local c2 = characters[u2]
        if not c2 then
            return
        end
        local w1 = c1.width  or 0
        local h1 = c1.height or 0
        local d1 = c1.depth  or 0
        local w2 = c2.width  or 0
        local h2 = c2.height or 0
        local d2 = c2.depth  or 0
        local mu = main.parameters.size/18
        characters[unicode] = {
            width    = w1,
            height   = h1 + h2 + d12*mu,
            depth    = d1,
            commands = {
                slotcommand[0][u1],
                leftcommand[w1/2 + w2/2],
                downcommand[-h1 + d2 -d12*mu],
                slotcommand[0][u2],
            }
        }
    end

    local function repeated(main,unicode,u,n,fraction)
        local characters = main.characters
        local c = characters[u]
        if c then
            if n == 1 then
               -- skip this one
            else
                local width  = c.width
                local italic = fraction*width -- c.italic or 0 -- larger ones have funny italics
                local tc     = slotcommand[0][u]
                local tr     = leftcommand[italic] -- see hack elsewhere
                local commands = { }
                for i=1,n-1 do
                    commands[#commands+1] = tc
                    commands[#commands+1] = tr
                end
                commands[#commands+1] = tc
                local next = c.next
                if next then
                    local p = addprivate(main,formatters["M-R-%H"](next))
                    repeated(main,p,next,n,fraction)
                    next = p
                end
                characters[unicode] = {
                    width       = width + (n-1)*(width-italic),
                    height      = c.height,
                    depth       = c.depth,
                    italic      = italic,
                    commands    = commands,
                    keepvirtual = true,
                    next        = next,
                }
            end
        end
    end

    local function extension(main,unicode,first,middle,last,ffactor,mfactor,lfactor)
        local characters = main.characters
        local chardata   = characters[unicode]
        if chardata then
            local fw = first  and characters[first]
            local mw = middle and characters[middle]
            local lw = last   and characters[last]
            if fw and lw then
                fw = fw.width ; if fw == 0 then fw = 1 end
                lw = lw.width ; if lw == 0 then lw = 1 end
                if middle == "left" then
                    chardata.parts = {
                        { extender = 0, glyph = first,  ["end"] = fw/2, start = 0,    advance = fw },
                        { extender = 1, glyph = last,   ["end"] = lw/2, start = lw/2, advance = lw },
                    }
                elseif middle == "right" then
                    chardata.parts = {
                        { extender = 1, glyph = first,  ["end"] = fw/2, start = fw/2, advance = fw },
                        { extender = 0, glyph = last,   ["end"] = lw/2, start = 0,    advance = lw },
                    }
                elseif mw then
                    mw = mw.width ; if mw == 0 then mw = 1 end
                    chardata.parts = {
                        { extender = 0, glyph = first,  ["end"] = fw/2, start = 0,    advance = (ffactor or 1)*fw },
                        { extender = 1, glyph = middle, ["end"] = mw/2, start = mw/2, advance = (mfactor or 1)*mw },
                        { extender = 0, glyph = last,   ["end"] = 0,    start = lw/2, advance = (lfactor or 1)*lw },
                    }
                end
                chardata.keepvirtual      = true -- why this issue with nested virtuals
                chardata.partsorientation = "horizontal"
            end
        end
    end

    vfmath.builders = {
        horibar    = horibar,
        rootbar    = rootbar,
        parent     = parent,
        brace      = brace,
        dots       = dots,
        jointwo    = jointwo,
        overlaytwo = overlaytwo,
        jointhree  = jointhree,
        stack      = stack,
        repeated   = repeated,
        extension  = extension,
    }

    -- todo: move this to the lfg files

end

local unique = 0 -- testcase: \startTEXpage \math{!\text{-}\text{-}\text{-}} \stopTEXpage

local reported = { }
local reverse  = { } -- index -> unicode

setmetatableindex(reverse, function(t,name)
    if trace_virtual then
        report_virtual("initializing math vector %a",name)
    end
    local m = mathencodings[name]
    local r = { }
    for u, i in next, m do
        r[i] = u
    end
    reverse[name] = r
    return r
end)

-- Used in fallbacks (might move):

local function copy_glyph(main,target,original,unicode,slot)
    local olddata = original[unicode]
    if olddata then
        local newdata = {
            width     = olddata.width,
            height    = olddata.height,
            depth     = olddata.depth,
            italic    = olddata.italic,
            topanchor = olddata.topanchor,
            kerns     = olddata.kerns,
            mathkerns = olddata.mathkerns,
            tounicode = olddata.tounicode,
         -- smaller   = olddata.smaller,
            commands  = { slotcommand[slot][unicode] },
        }
        local glyphdata = newdata
        local nextglyph = olddata.next
        while nextglyph do
            local oldnextdata = original[nextglyph]
            if oldnextdata then
                local newnextdata = {
                    width     = oldnextdata.width,
                    height    = oldnextdata.height,
                    depth     = oldnextdata.depth,
                    italic    = oldnextdata.italic,
                    topanchor = oldnextdata.topanchor,
                    kerns     = olddata.kerns,
                    mathkerns = olddata.mathkerns,
                    tounicode = olddata.tounicode,
                    smaller   = olddata.smaller,
                    commands  = { slotcommand[slot][nextglyph] },
                }
                local newnextglyph = addprivate(main,formatters["M-N-%H"](nextglyph),newnextdata)
                newdata.next = newnextglyph
                local nextnextglyph = oldnextdata.next
                if nextnextglyph == nextglyph then
                    break
                else
                    olddata   = oldnextdata
                    newdata   = newnextdata
                    nextglyph = nextnextglyph
                end
            else
                break -- safeguard (when testing stuff)
            end
        end
        local oldparts = olddata.parts
        if oldparts then
            newparts = fastcopy(oldparts)
            newdata.parts            = newparts
            newdata.partsorientation = olddata.partsorientation
            newdata.partsitalic      = olddata.partsitalic
            for i=1,#newparts do
                local newpart  = newparts[i]
                local oldglyph = newpart.glyph
                local olddata  = original[oldglyph]
                local newdata  = {
                    width     = olddata.width,
                    height    = olddata.height,
                    depth     = olddata.depth,
                    tounicode = olddata.tounicode,
                    commands  = { slotcommand[slot][oldglyph] },
                }
                newpart.glyph = addprivate(main,formatters["M-P-%H"](oldglyph),newdata)
            end
        end
        local smaller = olddata.smaller
        if smaller then
            local smallerdata = copy_glyph(main,target,original,smaller,slot)
            glyphdata.smaller = addprivate(main,formatters["M-S-%H"](smaller),smallerdata)
        end
        return glyphdata
    end
end

vfmath.copy_glyph = copy_glyph

-- It's time to get rid of this type 1 mess ... take iwona: uppercase /A .. Z but
-- lowercase /a.math ... /z.math ... anyway, we now follow a slightly different
-- route: use the "order" field. I can probably make it a bit leaner but it's not
-- worth spending much time on now.

local noitalics = true -- false can be used to test the engine

-- revision timestamp 2023: after watching ten times "Over The Mountain (feat.
-- Sierra Hull)" - Cory Wong (Live @ Brooklyn Steel FEB 2022):
--
-- https://www.youtube.com/watch?v=lT-W-UEcsns
-- https://www.youtube.com/watch?v=TPGbj1gFalA

-- The following code is now only used for iwona and antykwa, so I simplified it a
-- bit to suit that purpose. It might get even simpler.

local function virtualize(s,uni,fci,skewchar,move,mathparameters,unicode,parameters)
    if fci then
        local kerns   = fci.kerns
        local width   = fci.width
        local height  = fci.height
        local depth   = fci.depth
        local italic  = fci.italic
        local advance = width
        local bottomright
        local topanchor
        local yoffset
        if kerns and skewchar then
            local k = kerns[skewchar]
            if k then
                topanchor = width/2 + k
            end
        end
        if italic and noitalics then
            width       = width + italic
            bottomright = - italic
            italic      = nil
        end
        if move then  -- 0x222B
            local axis = move * mathparameters.axisheight
            local half = (height + depth ) / 2
            yoffset = depth - (half - axis)
            height = half + axis
            depth  = half - axis
        end
        --
        local next = fci.next
        return {
            advance          = advance,
            width            = width,
            height           = height,
            depth            = depth,
            italic           = italic,
            bottomright      = bottomright,
            topanchor        = topanchor,
            yoffset          = yoffset,
            commands         = { slotcommand[s][uni] },
         -- keepvirtual      = true,
            next             = fci.next,
            parts            = fci.parts,
            partsorientation = fci.partsorientation,
            partsitalic      = fci.partsitalic,
            unicode          = unicode,
            name             = fci.name,
        }
    else
        -- error
    end
end

function vfmath.define(specification,virtual,goodies)
    local name     = specification.name -- symbolic name
    local size     = specification.size -- given size
    local loaded   = { }
    local fontlist = { }
    local names    = { }
    local main     = nil
    local start    = (trace_virtual or trace_timings) and os.clock()
    local okset    = { }
    local n        = 0
    local f_extra  = formatters["virtual.extra.%05X"]
    local setlist  = virtual.recipe or virtual
    for s=1,#setlist do
        local ss     = setlist[s]
        local ssname = ss.name
        if add_optional and ss.optional then
            if trace_virtual then
                report_virtual("loading font %a subfont %s with name %a at %p is skipped",name,s,ssname,size)
            end
        else
            if ss.features then
                ssname = ssname .. "*" .. ss.features
            end
            if ss.main then
                main = s
            end
            local alreadyloaded = names[ssname] -- for px we load one twice (saves .04 sec)
-- local sshash = name .. ":" .. ssname
-- local alreadyloaded = names[sshash] -- for px we load one twice (saves .04 sec)
            local f, id
            if alreadyloaded then
                f, id = alreadyloaded.f, alreadyloaded.id
                if trace_virtual then
                    report_virtual("loading font %a subfont %s with name %a is reused",name,s,ssname)
                end
            else
                f, id = fonts.constructors.readanddefine(ssname,size)
                names[ssname] = {
-- names[sshash] = {
                    f        = f,
                    id       = id,
                    fontname = ssname, -- diagnostics
                }
            end
            if not f or id == 0 then
                report_virtual("loading font %a subfont %s with name %a at %p is skipped, not found",name,s,ssname,size)
            else
                n = n + 1
                okset[n] = ss
                loaded[n] = f
                fontlist[n] = {
                    id       = id,
                    size     = size,
                    fontname = ssname, -- diagnostics
                }
                if trace_virtual then
                    report_virtual("loading font %a subfont %s with name %a at %p as id %s using encoding %a",name,s,ssname,size,id,ss.vector)
                end
            end
        end
    end
    -- beware, loaded[1] is already passed to tex (we need to make a simple copy then .. todo)
    local parent         = loaded[1] or { } -- a text font
    local characters     = { }
    local parameters     = { }
    local mathparameters = { }
    local descriptions   = { }
    local metadata       = { }
    local properties     = {
        hasitalics = true,
        hasmath    = true,
    }
    if not goodies then
        goodies = { }
    end
    local main           = {
        metadata         = metadata,
        properties       = properties,
        characters       = characters,
        descriptions     = descriptions,
        parameters       = parameters,
        mathparameters   = mathparameters,
        fonts            = fontlist,
        goodies          = goodies,
        --
        fullname         = properties.fullname,
        nomath           = false,
    }
    --
    for key, value in next, parent do
        if type(value) ~= "table" then
            main[key] = value
        end
    end
    --
    if parent.characters then
        for unicode, character in next, parent.characters do
            characters[unicode] = character
        end
    else
        report_virtual("font %a has no characters",name)
    end
    --
    if parent.parameters then
        for key, value in next, parent.parameters do
            parameters[key] = value
        end
    else
        report_virtual("font %a has no parameters",name)
    end
    --
    local description = { name = "<unset>" }
    setmetatableindex(descriptions,function() return description end)
    --
    if parent.properties then
        setmetatableindex(properties,parent.properties)
    end
    --
    if parent.goodies then
        setmetatableindex(goodies,parent.goodies)
    end
    --
    local fullname = properties.fullname -- parent via mt
    if fullname then
        unique = unique + 1
        properties.fullname = fullname .. "-" .. unique
    end
    --
    if not parameters.xheight then
        parameters.xheight = 0
    end
    --
    local already_reported = false
    local parameters_done  = false
    local offset           = 0 -- 0xFF000 -- todo: -- private
    --
    for s=1,n do
        local ss = okset[s]
        local fs = loaded[s]
        if not fs then
            -- skip, error
        elseif add_optional and ss.optional then
            -- skip, redundant
        else
            local newparameters     = fs.parameters
            local newmathparameters = fs.mathparameters and ss.parameters ~= false
            if newmathparameters then
                if not parameters_done or ss.parameters then
                    mathparameters  = newmathparameters
                    parameters_done = true
                end
            elseif not newparameters then
                report_virtual("no parameters set in font %a",name)
            elseif ss.extension then
                mathparameters.xheight              = newparameters.xheight or 0 -- mathxheight          : height of x
                mathparameters.defaultrulethickness = newparameters[ 8]     or 0 -- defaultrulethickness : thickness of \over bars
                mathparameters.bigopspacing1        = newparameters[ 9]     or 0 -- bigopspacing1        : minimum clearance above a displayed op
                mathparameters.bigopspacing2        = newparameters[10]     or 0 -- bigopspacing2        : minimum clearance below a displayed op
                mathparameters.bigopspacing3        = newparameters[11]     or 0 -- bigopspacing3        : minimum baselineskip above displayed op
                mathparameters.bigopspacing4        = newparameters[12]     or 0 -- bigopspacing4        : minimum baselineskip below displayed op
                mathparameters.bigopspacing5        = newparameters[13]     or 0 -- bigopspacing5        : padding above and below displayed limits
            --  report_virtual("loading and virtualizing font %a at size %p, setting ex parameters",name,size)
            elseif ss.parameters then
                mathparameters.xheight    = newparameters.xheight
                                         or mathparameters.xheight
                                         or fs.xheight        or 0 -- xheight    : height of x
                mathparameters.num1       = newparameters[ 8] or 0 -- num1       : numerator shift-up in display styles
                mathparameters.num2       = newparameters[ 9] or 0 -- num2       : numerator shift-up in non-display, non-\atop
                mathparameters.num3       = newparameters[10] or 0 -- num3       : numerator shift-up in non-display \atop
                mathparameters.denom1     = newparameters[11] or 0 -- denom1     : denominator shift-down in display styles
                mathparameters.denom2     = newparameters[12] or 0 -- denom2     : denominator shift-down in non-display styles
                mathparameters.sup1       = newparameters[13] or 0 -- sup1       : superscript shift-up in uncramped display style
                mathparameters.sup2       = newparameters[14] or 0 -- sup2       : superscript shift-up in uncramped non-display
                mathparameters.sup3       = newparameters[15] or 0 -- sup3       : superscript shift-up in cramped styles
                mathparameters.sub1       = newparameters[16] or 0 -- sub1       : subscript shift-down if superscript is absent
                mathparameters.sub2       = newparameters[17] or 0 -- sub2       : subscript shift-down if superscript is present
                mathparameters.supdrop    = newparameters[18] or 0 -- supdrop    : superscript baseline below top of large box
                mathparameters.subdrop    = newparameters[19] or 0 -- subdrop    : subscript baseline below bottom of large box
                mathparameters.delim1     = newparameters[20] or 0 -- delim1     : size of \atopwithdelims delimiters in display styles
                mathparameters.delim2     = newparameters[21] or 0 -- delim2     : size of \atopwithdelims delimiters in non-displays
                mathparameters.axisheight = newparameters[22] or 0 -- axisheight : height of fraction lines above the baseline
            --  report_virtual("loading and virtualizing font %a at size %p, setting sy parameters",name,size)
            end
            -- We no longer care about kerns and ligatures here. We use backmap because we need to know
            -- the original order and the loader has made a unicode font of it and weird glyph names have
            -- spoiled that a bit too.
            if ss.overlay then
                -- This branch / option will go away.
                local fc    = fs.characters
                local first = ss.first
                if first then
                    local last = ss.last or first
                    for unicode = first, last do
                        characters[unicode] = copy_glyph(main,characters,fc,unicode,s)
                    end
                else
                    for unicode, data in next, fc do
                        characters[unicode] = copy_glyph(main,characters,fc,unicode,s)
                    end
                end
            else
                local vectorname = ss.vector
                if vectorname then
                    local vector      = mathencodings[vectorname]
                    local isextension = ss.extension
                    if vector then
                        local fc       = fs.characters
                        local fd       = fs.descriptions
                        local fp       = fs.parameters
                        local fontname = fs.properties.name or "unknown"
                        local skewchar = ss.skewchar
                        local backmap  = ss.backmap
                        local badones  = ss.badones
                        local ignore   = ss.ignore
                        local done     = { }
                        local extras   = { }
                        if backmap == false then
                         -- backmap = { }
                        elseif not backmap then
                            backmap = { }
                            for unicode, character in next, fc do
                                backmap[character.order or character.index or unicode] = unicode
                            end
                            ss.backmap  = backmap
                        end
                        for unicode, index in sortedhash(vector) do
                            local uni = backmap and backmap[index] or index
                            local fci = fc[uni]
                            if not fci then
                                local rf = reported[fontname]
                                if not rf then rf = { } reported[fontname] = rf end
                                local rv = rf[vectorname]
                                if not rv then rv = { } rf[vectorname] = rv end
                                local ru = rv[unicode]
                                if not ru then
                                    if trace_virtual then
                                        local d = chardata[unicode].description
                                        if index then
                                            report_virtual("character %C has no index %H in vector %a for font %a (%S)",unicode,index,vectorname,fontname,d)
                                        else
                                            report_virtual("character %C has no entry in vector %a for font %a (%S)",unicode,vectorname,fontname,d)
                                        end
                                    elseif not already_reported then
                                        report_virtual("the mapping is incomplete for %a at %p",name,size)
                                        already_reported = true
                                    end
                                    rv[unicode] = true
                                end
                            else
                                local name = fci.name or ""
                                if ignore and ignore[name] then
                                -- get rid of ugly slanted antykwa { }
                                else
                                    local u = mathematics.gaps[unicode] or unicode
                                    local t = virtualize(s,uni,fci,skewchar,tonumber(badones and badones[name]),mathparameters,u,fp)
                                    done[uni] = t
                                    characters[unicode] = t
                                    fci.unicode = u
                                end
                            end
                        end
--                         if ss.jmn then
--                             local extension = mathencodings["extensible-jmn-private"]
--                             for unicode, index in sortedhash(extension) do
--                                 if not characters[unicode] then
--                                     local uni = backmap and backmap[index] or index
--                                     local fci = fc[uni]
--                                     characters[unicode] = virtualize(s,uni,fci,skewchar,false,mathparameters,unicode,fp)
--                                 end
--                             end
--                         end
                        if isextension then
                            local extension = mathencodings["large-to-small"]
                            for uni, fci in sortedhash(fc) do
                                local name = fci.name or ""
                                if ignore and ignore[name] then
                                    -- get rid of ugly antykwa bar
                                elseif not done[uni] then
                                    local t = virtualize(s,uni,fci,skewchar,tonumber(badones and badones[name]),mathparameters,nil,fp)
                                    local o = addprivate(main,f_extra(offset))
                                    extras[uni] = o
                                    characters[o] = t
                                    done[uni] = t
                                    offset = offset + 1
                                end
                            end
                            for uni, fci in sortedhash(done) do
                                local next = fci.next
                                if next then
                                    fci.next = extras[backmap and backmap[next] or next]
                                end
                                local parts = fci.parts
                                if parts then
                                    local p = table.copy(parts)
                                    for i=1,#p do
                                        local part  = p[i]
                                        local glyph = part.glyph
                                        part.glyph  = extras[backmap and backmap[glyph] or glyph] or glyph
                                    end
                                    fci.keepvirtual      = true
                                    fci.parts            = p
                                    fci.partsorientation = "vertical" -- nasty as some are horizontal
                                    fci.partsitalic      = fci.partsitalic or fci.italic
                                end
                            end
                            for unicode, index in sortedhash(extension) do
                                local fci = characters[unicode]
                                if fci then
                                    fci.next = extras[backmap[index] or index]
                                end
                            end
                            local extension = mathencodings["large-to-small-private"]
                            for unicode, index in sortedhash(extension) do
                                if not characters[unicode] then
                                    local uni = backmap and backmap[index] or index
                                    local fci = fc[uni]
                                    characters[unicode] = virtualize(s,uni,fci,skewchar,false,mathparameters,unicode,fp)
                                end
                            end
                        end
                    else
                        report_virtual("error in loading %a, problematic vector %a",name,vectorname)
                    end
                end
            end
         -- mathematics.extras.copy(main) -- Not needed here (yet) ... might go.
        end
    end
    --
    main.mathparameters = mathparameters -- still traditional ones
    fontlist[#fontlist+1] = {
        id       = 0,
        size     = size,
        fontname = name, -- diagnostics
    }
    --
    local virtualtweaks = virtual.tweaks
    if virtualtweaks then
        --
        local mathtweaks  = mathematics.tweaks
        local knowntweaks = {
            addmissing = function(main,specification)
                local action = specification.action
                if action then
                    action(main,specification) -- source == target
                end
            end
        }
        --
        for i=1,#virtualtweaks do
            local specification = virtualtweaks[i]
            local tweak         = specification.tweak
            local action        = knowntweaks[tweak]
            if action then
                action(main,specification)
            else
                action = mathtweaks[tweak]
                if action then
                    action(main,main,specification)
                end
            end
        end
    end
    --
    mathematics.addfallbacks(main)
    --
    main.properties.math_is_scaled = true -- signal
    fonts.constructors.assignmathparameters(main,main)
    --
    mathematics.initializeparameters(main,main,"noscale")
    main.mathconstants = main.mathparameters -- we directly pass it to TeX (bypasses the scaler) so this is needed
    main.MathConstants = main.mathconstants
    main.nomath        = false
    --
    if trace_virtual or trace_timings then
        report_virtual("loading and virtualizing font %a at size %p took %0.3f seconds",name,size,os.clock()-start)
    end
    --
    return main
end

function mathematics.makefont(name,set,goodies)
    fonts.definers.methods.variants[name] = function(specification)
        return vfmath.define(specification,set,goodies)
    end
end

-- helpers (todo: gaps)

function vfmath.setletters(font_encoding, name, uppercase, lowercase)
    local enc = font_encoding[name]
    for i = 0,25 do
        enc[uppercase+i] = i + 0x41
        enc[lowercase+i] = i + 0x61
    end
end

function vfmath.setdigits(font_encoding, name, digits)
    local enc = font_encoding[name]
    for i = 0,9 do
        enc[digits+i] = i + 0x30
    end
end

-- local step = 0.2 -- 0.1 is nicer but gives larger files

-- local function clipped(main,characters,id,size,unicode,original) -- push/pop needed?
--     local minus = characters[original]
--     if minus then
--         local mu    = size/18
--         local step  = 3*mu
--         local width = minus.width
--         if width > step then
--             width = width - step
--             step  = step / 2
--         else
--             width = width / 2
--             step  = width
--         end
--         characters[unicode] = {
--             width    = width,
--             height   = minus.height,
--             depth    = minus.depth,
--             commands = {
--                 push,
--                 leftcommand[step],
--                 slotcommand[0][original],
--                 pop,
--             }
--         }
--     end
-- end

-- local function vertbar(main,characters,id,size,parent,scale,unicode)
--     local cp = characters[parent]
--     if cp then
--         local sc = scale * size
--         local pc = slotcommand[0][parent]
--         characters[unicode] = {
--             width    = cp.width,
--             height   = cp.height + sc,
--             depth    = cp.depth + sc,
--             next     = cp.next, -- can be extensible
--             commands = {
--                 push, upcommand  [sc], pc, pop,
--                 push, downcommand[sc], pc, pop,
--                                        pc,
--             },
--         }
--         cp.next = unicode
--     end
-- end

-- vertbar  (main,characters,id,size,0x0007C,0.10,0xFF601) -- big  : 0.85 bodyfontsize
-- vertbar  (main,characters,id,size,0xFF601,0.30,0xFF602) -- Big  : 1.15 bodyfontsize
-- vertbar  (main,characters,id,size,0xFF602,0.30,0xFF603) -- bigg : 1.45 bodyfontsize
-- vertbar  (main,characters,id,size,0xFF603,0.30,0xFF604) -- Bigg : 1.75 bodyfontsize
-- vertbar  (main,characters,id,size,0x02016,0.10,0xFF605)
-- vertbar  (main,characters,id,size,0xFF605,0.30,0xFF606)
-- vertbar  (main,characters,id,size,0xFF606,0.30,0xFF607)
-- vertbar  (main,characters,id,size,0xFF607,0.30,0xFF608)

-- clipped  (main,characters,id,size,0xFF501,0x0002D) -- minus
-- clipped  (main,characters,id,size,0xFF502,0x02190) -- lefthead
-- clipped  (main,characters,id,size,0xFF503,0x02192) -- righthead
-- clipped  (main,characters,id,size,0xFF504,ps("maps to piece") -- mapsto
-- clipped  (main,characters,id,size,0xFF505,0xFE322) -- lhook
-- clipped  (main,characters,id,size,0xFF506,0xFE323) -- rhook
-- clipped  (main,characters,id,size,0xFF507,0xFE324) -- mapsfrom
-- clipped  (main,characters,id,size,0xFF508,0x021D0) -- double lefthead
-- clipped  (main,characters,id,size,0xFF509,0x021D2) -- double righthead
-- clipped  (main,characters,id,size,0xFF50A,0x0003D) -- equal
-- clipped  (main,characters,id,size,0xFF50B,0x0219E) -- lefttwohead
-- clipped  (main,characters,id,size,0xFF50C,0x021A0) -- righttwohead
-- clipped  (main,characters,id,size,0xFF50D,0xFF350) -- lr arrow combi snippet
-- clipped  (main,characters,id,size,0xFF50E,0xFF351) -- lr arrow combi snippet
-- clipped  (main,characters,id,size,0xFF50F,0xFF352) -- lr arrow combi snippet
-- clipped  (main,characters,id,size,0xFF510,0x02261) -- equiv

-- extension(main,characters,id,size,0x2190,0xFF502,0xFF501,0xFF501) -- \leftarrow
-- extension(main,characters,id,size,0x2192,0xFF501,0xFF501,0xFF503) -- \rightarrow

-- extension(main,characters,id,size,0x002D,0xFF501,0xFF501,0xFF501)                 -- \rel
-- extension(main,characters,id,size,0x003D,0xFF50A,0xFF50A,0xFF50A)                 -- \equal
-- extension(main,characters,id,size,0x2261,0xFF510,0xFF510,0xFF510)                 -- \equiv

-- local lh = ps("left hook piece")]  -- was FE322
-- local rh = ps("right hook piece")] -- was FE323

-- jointwo  (main,characters,id,size,0x21A6,ps("maps to piece"),0,0x02192)                       -- \mapstochar\rightarrow
-- jointwo  (main,characters,id,size,0x21A9,0x02190,joinrelfactor,0xFE323)           -- \leftarrow\joinrel\rhook
-- jointwo  (main,characters,id,size,0x21AA,0xFE322,joinrelfactor,0x02192)           -- \lhook\joinrel\rightarrow
-- jointhree(main,characters,id,size,0x27FB,0x02190,joinrelfactor,0x0002D,0,0xFE324) -- \leftarrow\joinrel\relbar\mapsfromchar

-- jointhree(main,characters,id,size,0x27FC,ps("maps to piece"),0,0x0002D,joinrelfactor,0x02192) -- \mapstochar\relbar\joinrel\rightarrow

-- extension(main,characters,id,size,0x21A6,0xFF504,0xFF501,0xFF503) -- \mapstochar\rightarrow
-- extension(main,characters,id,size,0x21A9,0xFF502,0xFF501,0xFF506) -- \leftarrow\joinrel\rhook
-- extension(main,characters,id,size,0x21AA,0xFF505,0xFF501,0xFF503) -- \lhook\joinrel\rightarrow
-- extension(main,characters,id,size,0x27F5,0xFF502,0xFF501,0xFF501) -- \leftarrow\joinrel\relbar
-- extension(main,characters,id,size,0x27F6,0xFF501,0xFF501,0xFF503) -- \relbar\joinrel\rightarrow
-- extension(main,characters,id,size,0x27F7,0xFF502,0xFF501,0xFF503) -- \leftarrow\joinrel\rightarrow
-- extension(main,characters,id,size,0x27F8,0xFF508,0xFF50A,0xFF50A) -- \Leftarrow\joinrel\Relbar
-- extension(main,characters,id,size,0x27F9,0xFF50A,0xFF50A,0xFF509) -- \Relbar\joinrel\Rightarrow
-- extension(main,characters,id,size,0x27FA,0xFF508,0xFF50A,0xFF509) -- \Leftarrow\joinrel\Rightarrow
-- extension(main,characters,id,size,0x27FB,0xFF502,0xFF501,0xFF507) -- \leftarrow\joinrel\relbar\mapsfromchar
-- extension(main,characters,id,size,0x27FC,0xFF504,0xFF501,0xFF503) -- \mapstochar\relbar\joinrel\rightarrow

-- extension(main,characters,id,size,0x219E,0xFF50B,0xFF501,0xFF501) -- \twoheadleftarrow\joinrel\relbar
-- extension(main,characters,id,size,0x21A0,0xFF501,0xFF501,0xFF50C) -- \relbar\joinrel\twoheadrightarrow
-- extension(main,characters,id,size,0x21C4,0xFF50D,0xFF50E,0xFF50F) -- leftoverright